Tens of thousands marched through central London to protest against Government spending cuts.
Union leaders called it a building block towards a general strike.
Protests were also held in Belfast and Glasgow.
The Labour leader Ed Miliband launched a scathing attack on the Coalition Government in his address to an anti-austerity rally in Hyde Park, London.
He said: "The culture of two nations runs right across this government. They cut taxes for millionaires and raise them for ordinary people".
He made a joke at the expense of the Chancellor George Osborne who "tries to travel first class on a standard class ticket" and described the Prime Minister as "weak and clueless".
Speaking at the TUC rally Ed Miliband said: "It won't be easy choices, but they can be different choices. We can make different choices that put our young people back to work, that make our banks work for small businesses, that take real action on energy prices."
"I think what you see at this event today is a cross section of people from right across the country, who are worried about this government's approach."
Asked about a general strike Mr Miliband said: "I don't think that's the right thing to do and I don't think that's on the cards. I think what we need is a Labour government and that's what I'm going to be working for."
After the rally, a breakaway group caused a scuffle during a smaller demonstration outside the Savoy hotel.
The scuffle began after a protester took a doorman's hat.
The top hat was later returned to him.
No one is believed to have been seriously injured during the incident.